Download Natural Selection Lab 2

Natural Selection Lab 2
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The Process of Evolution
• Evolution is a change in gene frequency in a population
from generation to generation
• It is not the changing from an ape into a human…that
never happened
NO!!!
The Real Shape of Evolution
• Instead, think of evolution as a branching
tree, with everything connected
The Process of Evolution
• For a trait, count the number of organisms with each
form (different forms are called alleles) and you get the
frequency
• You have certain traits because of your genes, made up
of your DNA, which is the blueprint for your body
• The number of genes in a population that exists for each
form of a trait (like blood type or eye color) is the gene
frequency
• This is the basis for scientifically testing evolution
How Evolution Occurs
• How do frequencies change?
• Evolutionary forces:
• Migration is the flow of genes from one
population to the next
• Genetic drift is a skewed sample size from
one generation to the next
• Mutation: any change in the genes from one
population to the next
• Natural selection: individuals best suited to
their environment will survive and reproduce
Steps of Natural Selection
• More individuals are produced that can survive
• Variation means some are better adapted to
their environment
• Individuals compete for limited resources
• Those with better adapted traits will survive
and reproduce
• They thus pass down the better adapted genes
to future generations
• This is selective advantage
Evolutionary Theory as a Science
• Darwin knew evolution was a fact and set out
to create a theory explaining how it worked
• There are no alternatives to evolution that are
testable
• So, opponents who say that “evolution is just a
theory” are misusing the word theory.
Evolution is a fact…it has been tested
• However, all the mechanisms of how it works
are still being understood
https://www.youtube.com/watch?v=VwP_a4Ywz_8
CRASH COURSE DUDE
Evolution changes the
characteristics of a population, NOT
an individual
NO
x
YES
Time
The Vocabulary of Evolution
by Natural Selection
• Evolution: Change over time
• Natural Selection: Process by which species
evolve
• Reproductive Success: The number of offspring
an individual produces and rears to reproductive
age
• Fitness: A measure of relative reproductive
success
• Adaptation: An anatomical, physiological, or
behavioral trait which improves an organism’s
fitness in a given environment
• Selective Pressures: Forces in the environment
that influence reproductive success in individuals
Birds of the Galapagos show us
how natural selection works
Medium Ground
Finch
Daphne Major
Postulate 1: Environment constrains
population growth
• Severe
drought
occurred
1976-78
• Drought
affected seed
availability
and quality
• Many birds
died of
starvation
Postulate 2: Individuals vary in ability
to survive and reproduce
• Beak size varies
• Small beaked birds have trouble with large seeds
• During drought, larger beaked birds were at advantage
Postulate 3: Variation is transmitted
from parents to offspring
• Beak size is inherited
Characteristics of population changed
over time
• Large beaked adults survived better
• Large beaked birds had large beaked
offspring
• Mean beak size increased in population
TODAYS LAB
• EXERCISE 2: NATURAL SELECTION
– Read through Lab as a group
– Complete Lab by the end of today